VMware and Rapid Virtualization Indexing
Programmers and developers often use multiple operating systems to develop their programs for multiple platforms. Virtual machines provide a way to run multiple operating systems on the same hardware. Furthermore, server administrators often use virtual machines to run multiple network servers on the same computer. Running an operating system on top of another operating system inside a virtual machine might slow the main operating system, or the guest operating system or both. Rapid virtualization indexing attempts to address this by speeding up the performance of virtual machines.
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Virtual Machines
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Virtual machines provide a software layer between physical computer hardware and a guest operating system. The guest operating system runs inside the virtual machine software. As far as the guest in concerned, it has access to the computer's hardware. However, any hardware requests made by the guest must first go through the virtual machine, which then translates those requests into the language of the host operating system before communicating with hardware. So, for example, a Windows guest communicating with a monitor on a Linux operating system will send Input/Output signals as normal. The virtual machine will then translate those to Linux-specific requests which will be executed by the Linux OS.
VMWare Prior to RVI
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Essentially, having to translate been the virtual machine and host operating system could take some time. Regardless of the architecture of the guest operating system, the virtual machine has to decode system calls whenever they are made, and because system calls to hardware devices such as monitors or network controllers occur multiple times a second, this overhead can cause some slowdown. This slowdown becomes evident in the guest and host operating systems because they share these resources. The host OS must use the physical RAM of the system to process both the commands of the guest operating system through the virtual machine while running its own software and commands.
Rapid Virtualization Indexing
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Rapid virtualization indexing, also called "nested paging" during its development, offers hardware support of virtual machines to increase the speed of execution in virtual environments. "Nested paging" refers to a second level of paging tables between the hardware and the virtual machine. These tables reference memory in the virtual machine and allow for a quicker translation between machine and host OS. This means that instead of having the software take all of the overhead of translating commands to the CPU memory of the main host computer, the host computer processor aids in this by extending its memory to incorporate the virtual memory of the virtual machine.
VMWare Post-RVI
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After the implementation of RVI in AMD Quad-Core processors, performance in VMware software increased. Through a series of benchmarks, VMware shows that it has a significant increase in performance during Apache Web server compilation as well as under a kernel-testing benchmark suite known as "Kernel Microbenchmarks." The efficiency of paging support also improved according to the "SPECjbb200" Java benchmark. Overall, RVI technology offloads virtualization responsibility from the virtual machine to the hardware, increasing performance dramatically.
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